Two Pyrophosphates with Large Birefringences and Second‐Harmonic Responses as Ultraviolet Nonlinear Optical Materials

Abstract

Two new pyrophosphates nonlinear optical (NLO) materials, Rb3PbBi(P2O7)2 (I) and Cs3PbBi(P2O7)2 (II), were successfully designed and synthesized. Both compounds exhibit large NLO effects and birefringences. Material I presents the scarce case of possessing the coexistence of large birefringence (0.031 at 1064 nm and 0.037 at 532 nm) and second harmonic generation (SHG) response (2.8× potassium dihydrogen phosphate (KDP)) in ultraviolet NLO phosphates and its SHG is the largest in the phase‐matching (PM) pyrophosphates. Both I and II have three‐dimensional (3D) crystal structures composed of corner‐shared RbO12 (CsO11), RbO10 (CsO10), BiO6, PbO7 (PbO6) and P2O7 groups, in which P2O7 and PbO7 (PbO6) units form an alveolate [PbPO]∞ skeleton frame. Theoretical calculations reveal that the P−O, Bi−O and Pb−O units are mainly responsible for the moderate birefringence and large SHG efficiency of I.

Nonlinear Optical Oxythiophosphate Approaching the Good Balance with Wide Ultraviolet Transparency, Strong Second Harmonic Effect, and Large Birefringence

“…For decades, numerous attempts have been devoted in improving phosphates to realize a better balance among these key factors than KDP. In previous studies, on the one hand, by introducing various cations to coordinate with (PO 4 ) 3− , numerous NLO phosphates were discovered despite of still small birefringence, such as K 4 Mg 4 (P 2 O 7 ) 3 (Δ n ≈0.01), [5] K 2 SrP 4 O 12 (Δ n ≈0.02), [6] Ba 3 P 3 O 10 Cl (Δ n ≈0.03), [7] KLa(PO 3 ) 4 (Δ n ≈0.01), [8] Rb 3 PbBi(P 2 O 7 ) 2 (Δ n ≈0.03), [9] etc. On the other hand, by introducing fluorine anions into phosphate anionic units, fluorophosphates could exhibit enlarged birefringence, such as (NH 4 ) 2 PO 3 F (Δ n ≈0.03) [10] and NaNH 4 PO 3 F⋅H 2 O (Δ n ≈0.05), [11] although the promising balance including wide band gap, strong SHG effect and large birefringence have not been achieved.…”

A2BBi2(PO4)2(P2O7) (A = K, Rb, B = Pb, Cd): the Effect of Cation Sizes on Structural Evolution

“…Therefore, the IR spectra confirm the existence of PO 4 and P 2 O 7 units, which coincide with the results derived from the single-crystal X-ray structural analyses and previous reported phosphates. [17,25] Besides, the UV-vis-NIR diffuse reflectance spectra for I and II compounds were recorded. As described in Figure 7, the reflection rates of the two samples stay about 80 % in the measured region and the cut-off edges are all around 270 nm.…”

“…From Figure S6 we can see, the birefringence of II is about 0.018@1064 nm, which is smaller than that of Rb 3 PbBi(P 2 O 7 ) 2 (0.031@1064 nm), Cs 3 PbBi(P 2 O 7 ) 2 (0.020@1064 nm), Rb 2 PbBi 2 (PO 4 ) 2 (P 2 O 7 ) (0.021@1064 nm) and Cs 2 PbBi 2 (PO 4 ) 2 (P 2 O 7 ) (0.035@1064 nm). [17,18]…”

“…[16] Recently, we have successfully synthesized two pyrophosphates NLO materials containing Pb 2+ and Bi 3+ , A 3 PbBi(P 2 O 7 ) 2 (A = Rb, Cs) with good performances. [17] Based on the above-mentioned work, we obtained successfully two new compounds by cation modulation strategy, K 2 PbBi 2 -(PO 4 ) 2 (P 2 O 7 ) (I) and Rb 2 CdBi 2 (PO 4 ) 2 (P 2 O 7 ) (II) with two kinds of P-O groups simultaneously.…”

Nonlinear Optical Oxythiophosphate Approaching the Good Balance with Wide Ultraviolet Transparency, Strong Second Harmonic Effect, and Large Birefringence

“…For decades, numerous attempts have been devoted in improving phosphates to realize a better balance among these key factors than KDP. In previous studies, on the one hand, by introducing various cations to coordinate with (PO 4 ) 3À , numerous NLO phosphates were discovered despite of still small birefringence, such as K 4 Mg 4 (P 2 O 7 ) 3 (Dn % 0.01), [5] K 2 SrP 4 O 12 (Dn % 0.02), [6] Ba 3 P 3 O 10 Cl (Dn % 0.03), [7] KLa-(PO 3 ) 4 (Dn % 0.01), [8] Rb 3 PbBi(P 2 O 7 ) 2 (Dn % 0.03), [9] etc. On the other hand, by introducing fluorine anions into phosphate anionic units, fluorophosphates could exhibit enlarged birefringence, such as (NH 4 ) 2 PO 3 F (Dn % 0.03) [10] and NaNH 4 PO 3 F•H 2 O (Dn % 0.05), [11] although the promising balance including wide band gap, strong SHG effect and large birefringence have not been achieved.…”